EP2479391B1

EP2479391B1 - Exhaust gas purifying device and method for internal combustion engine

Info

Publication number: EP2479391B1
Application number: EP09849479.2A
Authority: EP
Inventors: Kazuhiro Itoh
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 2009-09-16
Filing date: 2009-09-16
Publication date: 2017-03-01
Anticipated expiration: 2029-09-16
Also published as: JPWO2011033620A1; WO2011033620A1; US20120174562A1; EP2479391A4; EP2479391A1; JP5382129B2; CN102482967B; US8857161B2; CN102482967A

Description

TECHNICAL FIELD

The present invention relates to an exhaust gas purification apparatus and an exhaust gas purification method for an internal combustion engine.

BACKGROUND ART

There has been known a technique in which an NOx sensor, a reducing agent supply device, and an NOx selective reduction catalyst are arranged in an exhaust passage of an internal combustion engine in a sequential manner from an upstream side thereof to a downstream side thereof (for example, see a first patent document).
Here, even if the NOx sensor is arranged at the upstream side of the reducing agent supply device, there is a fear that urea water as a reducing agent supplied from the reducing agent supply device may flow backwards to the vicinity of the NOx sensor due to the pulsation of exhaust gas, etc. When ammonia (NH₃) derived from urea adheres to the NOx sensor or exists in the vicinity of the NOx sensor, the ammonia may be detected by the NOx sensor, similar to NOx. On the other hand, the ammonia adhered to the NOx sensor may reduce NOx, thereby decreasing the concentration of NOx. If doing so, it will become difficult to detect the concentration of NOx in the exhaust gas in an accurate manner.
In addition, in cases where a temperature sensor is provided, if a liquid reducing agent is adhered to the temperature sensor or exists in the vicinity of the temperature sensor, heat in the surroundings of the temperature sensor is taken up by the reducing agent upon evaporation thereof, so it becomes difficult to detect the temperature of the exhaust gas in an accurate manner.
Further, in cases where a catalyst using HC as a reducing agent is provided, when the HC is added from the reducing agent supply device, it becomes difficult due to detect the air fuel ratio of the exhaust gas in an accurate manner due to the HC thus added.
The additive added in the exhaust gas adheres to a sensor in this manner, or there is a fear in the vicinity of a sensor that an error may occur in the detected value of the said sensor when it exists.

PRIOR ART REFERENCES

PATENT DOCUMENTS

First Patent Document: Japanese patent application laid-open No. 2007-170383
Second Patent Document: Japanese patent application laid-open No. 2009-121413
Third Patent Document: Japanese patent application laid-open No. 2009-024628

JP 2008 223681 discloses an exhaust emission control device.
JP 2009 127 497 discloses a diagnostic device of NOx cleaning device.

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

The present invention is made in view of the problems as mentioned above, and has for its object to provide a technique of suppressing the occurrence of an error in a detected value of a sensor due to an additive agent to be added into an exhaust gas.

MEANS FOR SOLVING THE PROBLEMS

In order to achieve the above-mentioned object, an exhaust gas purification apparatus for an internal combustion engine according to the present invention adopts the following units.
That is, the exhaust gas purification apparatus for an internal combustion engine according to the present invention comprises:

detection means that is arranged in an exhaust passage of the internal combustion engine for detecting a state of an exhaust gas;
addition means for adding an additive agent into said exhaust passage;
a catalyst that is arranged at the downstream side of said detection means and said addition means so as to receive a supply of the additive agent from said addition means;
determination means for determining whether detection accuracy of said detection means drops due to the additive agent to be added from said addition means; and
stop means for stopping the detection of the state of the exhaust gas by said detection means in cases where it is determined by said determination means that the detection accuracy of said detection means drops.

The detection means may be a sensor that detects a state of the exhaust gas, or may be a sensor that detects a concentration of a specific component in the exhaust gas. The addition means adds a reducing agent or an oxidizing agent as the additive agent. Then, this additive agent reacts in the catalyst arranged at the downstream side. By receiving a supply of the additive agent, the catalyst purifies the exhaust gas, or raises the temperature of the exhaust gas, or recovers its purification ability, for example.
Here, if the additive agent added from the addition means adheres to the detection means or exists in the vicinity of the detection means, the detection means will be affected by the influence of an the additive agent, as a result of which there will be a fear that the detection accuracy of the detection means may drop. In such a case, the stop means serves to stop the detection of the state of the exhaust gas by the detection means. Thus, it is possible to suppress the occurrence of an error in a detected value of the detection means. On the other hand, in cases where the detection means is not affected by the influence of the additive agent, there will be no error in the detected value of the detection means. For this reason, the detection accuracy of the detection means does not drop, so the detection of the state of the exhaust gas by the detection means is permitted.
Then, when the additive agent is added by said addition means, said determination means can make a determination that the detection accuracy of said detection means drops. This makes a determination that the detection accuracy drops or becomes lower as compared with the case in which the additive agent is not added by the addition means.
Here, when the additive agent is added by the addition means, there is a fear that the additive agent may flow toward the detection means. Even if the detection means is arranged at the upstream side of the addition means, the additive agent may flow toward the detection means due to the pulsation of the exhaust gas. If this additive agent adheres to the detection means or exists in the vicinity of the detection means, there will be a fear that the accuracy of the detection means may drop. In such a case, if it is determined that the accuracy of the detection means drops and the detection of the state of the exhaust gas is stopped, it will be possible to suppress the occurrence of an error in the detected value of the detection means.
Here, note that the longer a distance between the addition means and the detection means, the longer becomes a period of time until the additive agent added from the addition means reaches the detection means. Accordingly, the time or timing at which the detection accuracy of the detection means drops deviates or lags by this period of time. Thus, the timing at which the detection of the state of the exhaust gas is stopped may be decided according to a period of time after the additive agent is added until it reaches the detection means. Because this period of time is affected by the influence of the distance between the addition means and the detection means and the flow speed of the exhaust gas, for example, the timing to stop the detection of the state of the exhaust gas may be decided based on these factors. In this case, the determination means makes a determination that the detection accuracy of the detection means drops in a period of time which lags by a period of time taken until the additive agent moves from the addition means to the detection means, with respect to the period of time in which the additive agent is added from the addition means.
In addition, the more the amount of the additive agent adhering to the detection means, the longer becomes a period of time until all the additive agent evaporates. Accordingly, the timing at which the detection accuracy of the detection means drops deviates or lags by this period of time. Thus, the time or timing at which the detection of the state of the exhaust gas is stopped may be decided according to a period of time after the additive agent adheres to the detection means until it all evaporates. Because this period of time is affected by the influence of the timing of the additive agent and the amount of supply thereof, for example, the timing to stop the detection of the state of the exhaust gas may be decided based on these factors. In this case, the determination means makes a determination that the detection accuracy of the detection means drops in a period of time which is a sum of the period of time in which the additive agent is added from the addition means and the period of time until all the additive agent evaporates. In addition, the above-mentioned time lag may also be taken into consideration.
Moreover, provision can be made for estimation means for estimating the state of the exhaust gas of the internal combustion engine based on an operating state of the internal combustion engine,
wherein in cases where the detection of the state of the exhaust gas by said detection means is stopped by said stop means, the state of the exhaust gas can be estimated by said estimation means, instead of the detection of the state of the exhaust gas by said detection means.
If doing so, even when the detection of the state of the exhaust gas by the detection means is stopped, the state of the exhaust gas can be obtained by the provision of the estimation means. For example, in cases where the amount of addition of the additive agent is decided according to the state of the exhaust gas, the amount of addition of the additive agent can be decided according to an estimated value thereof, even during the time when the additive agent is being supplied. Here, note that the state of the exhaust gas changes, for example, according to the operating state of the internal combustion engine, so it is possible to estimate the state of the exhaust gas based on the operating state of the internal combustion engine.
According to the present invention, said catalyst may be composed to include an NOx selective reduction catalyst that serves to reduce the exhaust gas in a selective manner, and said detection means may be composed to include an NOx sensor that detects a concentration of NOx in the exhaust gas, and said addition means may add the reducing agent which is derived from ammonia.
In cases according to the present invention where the NOx sensor is adopted as the detection means, there is a fear that an error may occur in the detected value due to the detection of ammonia. On the other hand, in cases where a determination is made that the detection accuracy of the NOx sensor drops, if the detection of the concentration of NOx by the NOx sensor is stopped, it is possible to suppress the occurrence of an error in the detected value of the NOx sensor. Urea can be contained in the reducing agent.
Moreover, in an embodiment which is not covered by the present invention said detection means may be composed to include a temperature sensor that detects the temperature of the exhaust gas.
In cases where the temperature sensor is adopted as the detection means, the additive agent takes heat from the exhaust gas or the temperature sensor, so there will be a fear that an error may be caused in the detected value of the temperature sensor. On the other hand, in cases where a determination is made that the detection accuracy of the temperature sensor drops, if the detection of the temperature of the exhaust gas by the temperature sensor is stopped, it is possible to suppress the occurrence of an error in the detected value of the temperature sensor.
In order to achieve the above-mentioned object, an exhaust gas purification method for an internal combustion engine according to the present invention is defined by claim 4 and adopts the following means. That is, the exhaust gas purification method for an internal combustion engine according to the present invention comprises:

a first step to determine whether detection accuracy of a state of an exhaust gas drops due to the existence of an additive agent to be added to a catalyst at the time when the state of the exhaust gas of the internal combustion engine is detected; and
a second step to stop the detection of the state of the exhaust gas in cases where it is determined that the detection accuracy of the state of the exhaust gas drops.

Here, note that in said first step, when the additive agent is added, a determination can be made that the detection accuracy of the state of the exhaust gas drops.
In addition, the method may comprise including a third step to estimate the state of the exhaust gas, instead of the detection of the state of the exhaust gas, in cases where the detection of the state of the exhaust gas is stopped in said second step.

EFFECT OF THE INVENTION

According to the present invention, it is possible to suppress the occurrence of an error in a measured value of a sensor due to an additive agent added into exhaust gas.

BRIEF DESCRIPTION OF THE DRAWINGS

[Fig. 1] is a view showing the schematic construction of an exhaust gas purification apparatus for an internal combustion engine according to a first and a second embodiment of the present invention.
[Fig. 2] is a flow chart showing a control flow according to the first embodiment.
[Fig. 3] is a flow chart showing a control flow according to the second embodiment.
[Fig. 4] is a view showing the schematic construction of an exhaust gas purification apparatus for an internal combustion engine according to a third embodiment of the present invention.

MODES FOR CARRYING OUT THE INVENTION

Hereinafter, reference will be made to specific modes of embodiments of an exhaust gas purification apparatus and an exhaust gas purification method for an internal combustion engine according to the present invention based on the attached drawings.

First Embodiment

Fig. 1 is a view showing the schematic construction of an exhaust gas purification apparatus for an internal combustion engine according to this first embodiment of the present invention. An internal combustion engine 1 shown in Fig. 1 is a four-cycle diesel engine of a water cooled type having four cylinders. Here, note that the following embodiments can be applied even to a gasoline engine in a similar manner.
An exhaust passage 2 is connected to the internal combustion engine 1. In the exhaust passage 2, there are arranged a sensor 4, an addition valve 5, and a catalyst 3 in a sequential manner from an upstream side in the direction of flow of an exhaust gas.
In addition, the sensor 4 is to detect a state of the exhaust gas, and it detects, for example, a concentration of a specific component in the exhaust gas. As the sensor 4, there can be mentioned, for example, an air fuel ratio sensor, an oxygen concentration sensor, an HC sensor, or an NOx sensor. In addition, the sensor 4 may be, for example, a temperature sensor that detects a temperature of the exhaust gas. Here, note that in this embodiment, the sensor 4 corresponds to detection means in the present invention.
The addition valve 5 injects an additive agent such as a reducing agent, an oxidizing agent or the like. For the additive agent, there can be used, for example, fuel (HC), or a reducing agent derived from ammonia, such as urea water, or the like. What is used for the additive agent is decided according to the kind of catalyst 3. Then, the additive agent reacts in the catalyst 3. Here, note that in this embodiment, the addition valve 5 corresponds to addition means in the present invention.
As the catalyst 3, there can be mentioned, for example, an NOx storage reduction catalyst, an NOx selective reduction catalyst, an oxidation catalyst, or a three-way catalyst. In addition, a particulate filter may be provided in which these catalysts are supported, or are arranged at a location upstream thereof.
In the internal combustion engine 1 constructed as stated above, there is arranged in combination therewith an ECU 10 which is an electronic control unit for controlling the internal combustion engine 1. This ECU 10 is a unit that controls the operating state of the internal combustion engine 1 in accordance with the operating conditions of the internal combustion engine 1 and/ or driver's requirements.
The above-mentioned sensors, an accelerator opening sensor 12, which is able to detect an engine load by outputting an electrical signal corresponding to an amount by which a driver depressed an accelerator pedal 11, and a crank position sensor 13, which detects the number of revolutions per unit time of the engine, are connected to the ECU 10 through electrical wiring, and the output signals of these variety of kinds of sensors are inputted to the ECU 10. On the other hand, the addition valve 5 is connected to the ECU 10 through electrical wiring, so that the addition valve 5 is controlled by the ECU 10.
Here, note that in this embodiment, description will be made on the following assumptions. The sensor 4 is an NOx sensor; the addition valve 5 is to add urea water; and the catalyst 3 is an NOx selective reduction catalyst. According to such assumptions, the urea water added from the addition valve 5 is hydrolyzed by the heat of the exhaust gas, as a result of which ammonia (NH₃) is produced, and a part or all thereof adsorbs to the catalyst 3. This ammonia serves to reduce NOx in a selective manner. Then, by supplying the ammonia to the catalyst 3 or by making it to be adsorbed thereto beforehand, NOx is made to be reduced during the time when the NOx passes through the catalyst 3.
Then, in order to make ammonia to be adsorbed to the catalyst 3 beforehand, urea water is added from the addition valve 5 in an intermittent manner. For example, the concentration of NOx is detected by the sensor 4, and the amount of NOx is calculated from the NOx concentration thus detected and the amount of intake air. The amount of ammonia adsorbed to the catalyst 3 decreases according to this amount of NOx, so the urea water is added from the addition valve 5 at the time when the amount of ammonia adsorbed to the catalyst 3 becomes equal to or less than a prescribed amount. Here, note that the interval at which the urea water is added from the addition valve 5 may be set to a constant value, and the amount of the urea water to be added from the addition valve 5 may be decided according to the NOx concentration obtained by the sensor 4. In this manner, the urea water is added intermittently.
Here, there is a fear that the urea water added into the exhaust gas from the addition valve 5 may flow backwards up to the vicinity of the sensor 4 due to the pulsation of the exhaust gas. In the case of the NOx sensor, ammonia as well as NOx may be detected by a catalyst coated on the NOx sensor, and hence, if ammonia exists in the areas surrounding the NOx sensor, there will be a fear that the concentration of NOx may be detected to be higher than an actual value thereof. On the other hand, if the urea water adheres to the sensor 4, the NOx in the exhaust gas may be reduced by means of the catalyst coated on the sensor 4, so there will be a fear that the concentration of NOx may be detected to be lower than the actual value thereof. In this manner, an error may occur in the detected value of the sensor 4 due to the addition of the urea water. In contrast to this, in this embodiment, at the time when urea water is added into the exhaust gas from the addition valve 5, the detection of the concentration of NOx by the sensor 4 is stopped.
Fig. 2 is a flow chart showing a control flow or routine according to this first embodiment. This routine is carried out by means of the ECU 10 in a repeated manner at each predetermined time interval.
In step S101, it is determined whether urea water is added from the addition valve 5. That is, it is determined whether the sensor 4 is in a state where there is a fear that an error may occur in the detected value of the sensor 4. In cases where an affirmative determination is made in step S101, the routine advances to step S102, whereas in cases where a negative determination is made, the routine advances to step S103. Here, note that in this embodiment, the ECU 10, which carries out the processing of step S101, corresponds to determination means in the present invention. Also, in this embodiment, the step S101 corresponds to a first step in the present invention.
In step S102, the detection of the concentration of NOx by the sensor 4 is stopped. On the other hand, in step S103, the detection of the concentration of NOx by the sensor 4 is permitted. Here, note that in this embodiment, the ECU 10, which carries out the processing of step S102, corresponds to stop means in the present invention. Also, in this embodiment, the step S102 corresponds to a second step in the present invention.
In this manner, when urea water is added from the addition valve 5, the detection of the concentration of NOx by the sensor 4 is stopped, whereas when urea water is not added, the detection of the concentration of NOx by the sensor 4 is permitted.
Here, note that in this embodiment, the detection of the concentration of NOx by the sensor 4 is stopped in a period of time in which urea water is added from the addition valve 5, but instead of this, the detection of the concentration of NOx by the sensor 4 may be stopped in a period of time in which the urea water is actually adhered to the sensor 4, or in a period of time in which the urea water actually exists in the areas surrounding the sensor 4. That is, the time taken until the urea water added from the addition valve 5 reaches the sensor 4 may be taken into consideration, or the time taken until the urea water adhered to the addition valve 5 evaporates may be taken into consideration. These periods of time have correlation with, for example, the amount of addition of urea water, the timing or time of addition of urea water, the flow rate of the exhaust gas, and the distance from the addition valve 5 to the sensor 4, and hence can be obtained based on the values of these factors. Such correlation may have beforehand been obtained through experiments, etc., made into a map, and stored in the ECU 10.
Here, note that in this embodiment, the detection of the concentration of NOx by the sensor 4 may be stopped, for example, at the time when the flow speed of the exhaust gas is equal to or less than a specified value and in the period of time in which urea water is added from the addition valve 5. In this case, when the flow speed of the exhaust gas exceeds the specified value, the detection of the concentration of NOx by the sensor 4 is permitted even in the period of time in which urea water is added from the addition valve 5. Here, the higher the flow speed of the exhaust gas, the more difficult it becomes for the urea water to adhere to the sensor 4. In addition, the higher the flow speed of the exhaust gas, the more difficult it becomes for the urea water to flow backwards. Then, even if urea water is added, the detected value of the sensor 4 may not be affected, depending on the flow speed of the exhaust gas. In such a case, it is possible to permit the detection of the concentration of NOx even at the time of adding urea water. As a result of this, it is possible to suppress the detection of the concentration of NOx from being stopped even when it is unnecessary. The specified value has been beforehand obtained as a flow speed at which urea water does not adhere to the sensor 4 or does not exist in the vicinity of the sensor 4. Here, note that the flow rate of the exhaust gas or the space velocity (SV) thereof may be used in place of the flow speed of the exhaust gas.
Here, note that in the case where the sensor 4 is a temperature sensor, heat is taken from the exhaust gas and the sensor 4 at the time when the additive agent added from the addition valve 5 evaporates, so the temperature of the exhaust gas and the temperature of the sensor 4 are caused to decrease. If temperature detection is made by the sensor 4 at this time, a temperature lower than the original or actual temperature of the exhaust gas will be detected. On the other hand, if the detection of the temperature of the exhaust gas by the sensor 4 is stopped when the additive agent is added from the addition valve 5, it is possible to suppress the occurrence of an error in the detected value of the temperature of the exhaust gas.
In addition, in cases where the sensor 4 is an air fuel ratio sensor and the additive agent is HC, the HC added from the addition valve 5 affects the detected value of the air fuel ratio sensor. On the other hand, if the detection of the air fuel ratio by the air fuel ratio sensor is stopped when HC is added from the addition valve 5, it is possible to suppress the occurrence of an error in the detected value of the air fuel ratio. If doing so, the amount of addition of HC can be rationalized, so it is possible to suppress the catalyst 3 from being poisoned and overheated by HC. Moreover, it is also possible to suppress the generation of hydrogen sulfide due to the air fuel ratio becoming excessively low.
Here, note that in this embodiment, the addition valve 5 is arranged at the downstream side of the sensor 4 in the direction of flow of the exhaust gas, but instead of this, even in cases where the addition valve 5 is arranged at the upstream side of the sensor 4, the present invention can be applied in a similar manner. In addition, the addition valve 5 may also be arranged at a position which has no difference from that of the sensor 4 in the direction of flow of the exhaust gas.
As described above, according to this embodiment, when the additive agent is added from the addition valve 5, the detection of the state of the exhaust gas by the sensor 4 is stopped, so it is possible to suppress the occurrence of an error in the detected value of the sensor 4. Accordingly, an appropriate amount of additive agent can be added, and hence, it is possible to suppress a drop in exhaust gas purification performance due to a shortage of the additive agent. In addition, the additive agent becomes surplus or excessive, thereby making it possible to suppress the additive agent from passing sideways through the catalyst 3.

Second Embodiment

In this second embodiment, when the additive agent is added from the addition valve 5, the detection of the state of the exhaust gas by the sensor 4 is stopped, and at the same time, the state of the exhaust gas is estimated from the operating state of the internal combustion engine 1, and the thus estimated value is used instead of the detected value obtained by the sensor 4. The other devices, parts and so on are the same as those in the first embodiment, so the explanation thereof is omitted.
When the additive agent is added from the addition valve 5, the detection of the state of the exhaust gas by the sensor 4 is stopped. This is carried out in the same manner as in the first embodiment, so an explanation thereof is omitted. Then, the state of the exhaust gas is estimated in the following manner. Here, note that what is to be estimated at this time is the same as that to be detected by the sensor 4.
Here, the state of the exhaust gas is affected, for example, by the influences of the number of engine revolutions per unit time, the degree of opening of the accelerator pedal, the amount of fuel injection, fuel injection timing, the throttle opening degree, the intake air temperature, the amount of intake air, the atmospheric pressure, and so on. In addition, in cases where provision is made for an EGR (Exhaust Gas Recirculation) system for supplying a part of the exhaust gas to the intake passage, the state of the exhaust gas is also affected by the influences of the degree of opening of an EGR valve which adjusts the flow rate of an EGR gas, and the temperature of an EGR cooler which carries out cooling of the EGR gas. Moreover, in cases where a turbocharger is provided, the state of the exhaust gas is further affected by the influences of the supercharging pressure and the number of revolutions per unit time of the turbocharger. In cases where a variable volume type turbocharger is provided, the state of the exhaust gas is affected by the influence of the degree of opening of nozzle banes thereof. Here, note that there are some ones which are not affected by any influence, depending on what is to be estimated.
That is, the state of the exhaust gas can be estimated based on those which have correlation with what is to be estimated, among these values. Such correlation may have beforehand been obtained through experiments, etc., and made into a map.
Fig. 3 is a flow chart showing a control flow or routine according to this second embodiment. This routine is carried out by means of the ECU 10 in a repeated manner at each predetermined time interval. Here, note that description will be made on the following assumptions. The addition valve 5 is to add urea water, and the catalyst 3 is an NOx selective reduction catalyst. Also, note that for those steps in which the same processing as in the flow shown in Fig. 2 is carried out, the same symbols are attached and an explanation thereof is omitted. Then, in the flow shown in Fig. 3, in step S201, the concentration of NOx is estimated. If the amount of addition of urea water and the timing of addition thereof are decided based on the concentration of NOx estimated in this manner, an appropriate amount of additive agent can be added at an appropriate timing. Here, note that in this embodiment, the ECU 10, which carries out the processing of step S201, corresponds to estimation means in the present invention. Also, in this embodiment, the step S201 corresponds to a third step in the present invention.
As described above, according to this second embodiment, when the additive agent is added from the addition valve 5, the detection of the state of the exhaust gas by the sensor 4 is stopped, so it is possible to suppress the occurrence of an error in the detected value of the sensor 4. Moreover, at this time, it is possible to obtain the state of the exhaust gas according to the estimation thereof. As a result of this, it is possible to attain the rationalization of the amount of addition and the timing of addition of the additive agent.

Third Embodiment

Fig. 4 is a view showing the schematic construction of an exhaust gas purification apparatus for an internal combustion engine according to this third embodiment of the present invention. Mainly, those which are different from Fig. 1 will be explained.
In this embodiment, an oxidation catalyst 21 and a particulate filter 22 (hereinafter referred to simply as a filter 22) are arranged in the exhaust passage 2 at the upstream side of the sensor 4 and the addition valve 5. The filter 22 traps PM (particulate matter) contained in the exhaust gas. Then, when the particulate matter trapped by the filter 22 is oxidized, the temperature of the filter 22 is caused to rise by supplying, for example, HC to the oxidation catalyst 21. Here, note that for the oxidation catalyst 21, there can be used another catalyst having an oxidation function, such as for example a three-way catalyst, an NOx storage reduction catalyst, etc. In addition, the oxidation catalyst 21 may be supported on the filter 22.
The addition valve 5 and the sensor 4 are mounted or arranged in the exhaust passage 2 at locations immediately downstream of the filter 22. The addition valve 5 is arranged at the downstream side of the sensor 4 in the direction of flow of the exhaust gas, or at a location that has no difference from (i.e., is identical with) that of the sensor 4 in the direction of flow of the exhaust gas. That is, the addition valve 5 is arranged at a location at which the sensor 4 is not positioned at the downstream side of the addition valve 5 in the direction of flow of the exhaust gas. In addition, the addition valve 5 and the sensor 4 are arranged at locations at which the channel cross sections of the exhaust passage 2 are made relatively large, so as to reduce a pressure loss in the filter 22.
With such an arrangement, the distance from the addition valve 5 to the catalyst 3 can be made long, and the channel cross sectional area of the exhaust passage 2 is decreased and increased, so that the additive agent can be dispersed in a wide range, as a result of which the concentration of the additive agent can be made uniform. According to this, the purification of the exhaust gas in the catalyst 3 can be facilitated.
However, the distance of the addition valve 5 and the sensor 4 becomes short, so that the sensor 4 becomes easy to be affected by the influence of the additive agent added from the addition valve 5.
On the other hand, similar to the first embodiment, when the additive agent is added from the addition valve 5, the detection of the state of the exhaust gas by means of the sensor 4 is stopped. In addition, similar to the second embodiment, when the additive agent is added from the addition valve 5, the detection of the state of the exhaust gas by the sensor 4 may be stopped, and at the same time, the state of the exhaust gas may be estimated from the operating state of the internal combustion engine 1. In this manner, it is possible to suppress the occurrence of an error in the detected value of the sensor 4, while enhancing the exhaust gas purification performance.

EXPLANATION OF REFERENCE NUMERALS AND CHARACTERS

1: internal combustion engine
2: exhaust passage
3: catalyst
4: sensor
5: addition valve
10: ECU
11: accelerator pedal
12: accelerator opening sensor
13: crank position sensor
21: oxidation catalyst
22: particulate filter

Claims

An exhaust gas purification apparatus for an internal combustion engine (1) comprising:
detection means (4) that is arranged in an exhaust passage (2) of the internal combustion engine (1) for detecting a state of an exhaust gas;

addition means (5) for adding an additive agent into said exhaust passage;

a catalyst (3) that is arranged at the downstream side of said detection means and said addition means so as to receive a supply of the additive agent from said addition means;

determination means (10) adapted to determine whether detection accuracy of said detection means drops due to the additive agent to be added from said addition means; and

stop means (10) adapted to stop the detection of the state of the exhaust gas by said detection means in cases where it is determined by said determination means that the detection accuracy of said detection means drops,
characterized in that said catalyst (3) is composed to include an NOx selective reduction catalyst that serves to reduce the exhaust gas in a selective manner; said detection means (4) is composed to include an NOx sensor that detects a concentration of NOx in the exhaust gas; and said addition means adds the reducing agent derived from ammonia.
The exhaust gas purification apparatus for an internal combustion engine (1) as set forth in claim 1, characterized in that said determination means (10) is adapted to determine that the detection accuracy of said detection means (4) drops when the additive agent is added by said addition means (5).
The exhaust gas purification apparatus for an internal combustion engine (1) as set forth in claim 1 or 2, characterized by further comprising:
estimation means (10, 12, 13) adapted to estimate the state of the exhaust gas of the internal combustion engine based on an operating state of the internal combustion engine (1);

wherein in cases where the detection of the state of the exhaust gas by said detection means is stopped by said stop means, the state of the exhaust gas is estimated by said estimation means, instead of the detection of the state of the exhaust gas by said detection means.
An exhaust gas purification method for an internal combustion engine (1), characterized by comprising:
a first step to determine whether detection accuracy of a state of an exhaust gas drops due to the existence of an additive agent derived from ammonia to be added to a catalyst at the time when the state of the exhaust gas (2) of the internal combustion engine (1) is detected, said catalyst being composed to include an NOx selective reduction catalyst that serves to reduce the exhaust gas in a selective manner, wherein the detection of the state of the exhaust gas detects a concentration of NOx in the exhaust gas; and

a second step to stop the detection of the state of the exhaust gas in cases where it is determined that the detection accuracy of the state of the exhaust gas drops.
The exhaust gas purification method for an internal combustion engine as set forth in claim 4, characterized in that in said first step, when the additive agent is added, a determination is made that the detection accuracy of the state of the exhaust gas drops.
The exhaust gas purification method for an internal combustion engine as set forth in claim 4 or 5, characterized by further comprising:
a third step to estimate the state of the exhaust gas, instead of the detection of the state of the exhaust gas, in cases where the detection of the state of the exhaust gas is stopped in said second step.